SummaryQuantifying the dimensions and magnitude of intraspecific root trait variation is key to understanding the functional trade-offs in the belowground plant strategies of tropical forest trees. Additionally, accurately measuring how belowground functional trait variation relates to soil environment and forest age is crucial to tropical forest modeling efforts.We sampled leaf and root morphologies from 423 juvenile trees of 72 species from 14 Angiosperm families along a 6.6 km transect that corresponded to an environmental gradient in decreasing soil fertility and texture with increasing forest age.We observed within-lineage conservative functional trait-shifts in root and leaf morphological traits along the transect. From secondary to primary forest, average leaf area increased 7 cm2and average root system diameter increased 0.4 mm. Mean specific leaf area decreased by 0.8 m2kg−1, specific root length decreased by 3.5 m kg−1, and root branching intensity decreased by 0.3 tips cm−1. Leaf thickness and root tissue density showed no change.We coupled trait measurements to a network of 164 1/16th-ha plots across a Chinese tropical forest reserve, to scale individual trait measurements up to the community-level, accounting for forest age.For most traits, intraspecific trait variation negatively covaried with species compositional turnover between plots in younger versus older forest to compound and create greater community-weighted differences in trait values than would be observed if intraspecific variation in traits with forest age was not accounted for.SummaryRoot morphologies are variable with local scale variation in soil fertility and texture. Accurately understanding broader (i.e. forest)-scale patterns in root functional traits, requires attention to underlying environmental variation in soil resources, which interacts with environmental filtering of plant communities.
The mechanism proposed to explain tree monodominance in tropical forests is that the dominant species forms a dense canopy and produces shade-tolerant seedlings, which together favor selfreplacement. Under this hypothesis, seedlings of monodominant species should have limited ability to respond to drastic increases in understory light, like those resulting from logging. Therefore, monodominant species should lose their seedling dominance after logging-induced canopy opening. To test this hypothesis, the current study measured seedling survival and growth of the monodominant species, Prioria copaifera, and its main competitor, Pentaclethra macroloba, in two forest stands that differ in logging history and in an unlogged stand in southeastern Costa Rica. Although, growth rates and survival of previously established seedlings were similar for both species across the three stands, seedling survival and growth decreased as light increased, with the effect being more pronounced for Prioria than for Pentaclethra. The study also investigated the ability of Prioria to respond to changing light environments by transplanting seedlings into logging-induced canopy gaps. Contrary to prediction, Prioria seedlings survived and grew better in gap centers than in gap edges or under a closed canopy. This result contrasts with established seedlings that cannot acclimate to changes in light conditions. Therefore, we conclude that continued Prioria dominance in selectively logged forests depends more on seedling production after canopy disturbance than on the established seedling present before disturbances.
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